Tropical Storm KHANUN Advisory Sat Oct 14

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (KHANUN)
WARNING NR 05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 24W (KHANUN), LOCATED APPROXIMATELY 621 NM
EAST OF DA NANG, VIETNAM, HAS TRACKED WESTWARD AT 16 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A LOW-
LEVEL CIRCULATION CENTER (LLCC) WHICH CONTINUES TO CONSOLIDATE.
EXTENSIVE CONVECTIVE BANDING IN THE LUZON STRAIT CONTINUES TO WRAP
INTO THE LLCC. A 130656Z GMI 37GHZ COMPOSITE IMAGE SHOWS THE
SYSTEM IS CONTINUING TO IMPROVE IN OVERALL STRUCTURE WITH THE LLCC
LOCATED TO THE WEST OF LUZON. THE INITIAL INTENSITY IS ASSESSED AT
45 KNOTS BASED ON A DVORAK ESTIMATE OF T3.0 (45 KNOTS) FROM PGTW.
UPPER-LEVEL ANALYSIS DEPICTS A GENERALLY FAVORABLE ENVIRONMENT WITH
MODERATE VERTICAL WIND SHEAR (20 TO 25 KNOTS). POLEWARD AND
EQUATORWARD OUTFLOW BOTH REMAIN EXCELLENT AND SEA SURFACE
TEMPERATURES REMAIN WARM (29-30 CELSIUS). TS 24W IS UNDER THE
STEERING INFLUENCE OF THE EAST-WEST ORIENTED SUBTROPICAL RIDGE (STR)
ENTRENCHED TO THE NORTH.
3. FORECAST REASONING.
     A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE. THE 34-KNOT WIND RADII REMAIN
EXTENSIVE THROUGH TAU 48 DUE TO THE INTERACTION WITH THE STRONG
NORTHEASTERLY SURGE FLOW.
     B. TS 24W WILL TRACK WEST-NORTHWESTWARD AS IT REMAINS ON THE
SOUTHWESTERN PERIPHERY OF THE DEEP-LAYERED STR. THE STR WILL REMAIN
THE PRIMARY STEERING MECHANISM THROUGHOUT THE FORECAST. HOWEVER, A
SLIGHT WEAKENING IN THE STR WILL ALLOW THE TRACK OF TS 24W TO BECOME
WEST-NORTHWESTWARD AS IT TRANSITS THE SOUTH CHINA SEA. TS 24W WILL
ALSO INCREASE IN INTENSITY AS IT TRACKS ACROSS WARM SEA SURFACE
TEMPERATURES WITH FAVORABLE UPPER-LEVEL CONDITIONS. BY TAU 36 THE
INTENSITY WILL INCREASE TO 75 KNOTS AS TS 24W APPROACHES HAINAN
ISLAND. NUMERICAL MODEL GUIDANCE IS GENERALLY IN GOOD AGREEMENT WITH
A WEST-NORTHWESTWARD TRACK. HOWEVER, THERE IS NOW A GREATER SPREAD
IN THE MODEL TRACK FORECASTS WHEN COMPARED TO PREVIOUS MODEL RUNS.
     C. IN THE EXTENDED PERIOD, TS 24W WILL TRACK WESTWARD AND WILL
MAKE A SECOND LANDFALL IN NORTHERN VIETNAM NEAR TAU 84 AND WILL
WEAKEN RAPIDLY AS IT MOVES INLAND. OVERALL, DYNAMIC MODEL GUIDANCE
IS IN GOOD AGREEMENT UNTIL AFTER TAU 96 WHERE SEVERAL MODELS
ERRONEOUSLY SHOW THE REMNANTS OF TS 24W TURNING SHARPLY SOUTHWARD.
THE STR LOCATED TO THE NORTH IS EXPECTED TO REMAIN STRONG ENOUGH
DURING THIS TIME PERIOD TO KEEP THE TRACK MORE WESTWARD. OVERALL
THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.//
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